Outcome of extracranial malignant rhabdoid tumours in children registered in the European Paediatric Soft Tissue Sarcoma Study Group Non-Rhabdomyosarcoma Soft Tissue Sarcoma 2005 Study-EpSSG NRSTS 2005.

Background: Extracranial malignant rhabdoid tumours (MRT) are rare lethal childhood cancers that often occur in infants and have a characteristic genetic mutation in the SMARCB1 gene. The European Paediatric Soft Tissue Sarcoma Study Group (EpSSG) conducted a multinational prospective study of registered cases of extracranial MRT to test an intensive multimodal approach of treatment for children with newly diagnosed extracranial MRT.

Methods: Between December 2005 and June 2014, we prospectively registered 100 patients from 12 countries with a diagnosis of MRT tumour at an extracranial site on the EpSSG Non-Rhabdomyosarcoma Soft Tissue Sarcoma 2005 Study (NRSTS 2005). They were all treated on a standard multimodal protocol of surgery, radiotherapy, and chemotherapy over 30 weeks as follows: vincristine, cyclophosphamide, and doxorubicin (VDCy) at weeks 1, 10, 13, 22, and 28; vincristine was also given alone on weeks 2, 3, 11, 12, 14, 15, 23, 24, 29, and 30. Cyclophosphamide, carboplatin, and etoposide (Cy*CE) was given at weeks 4, 7, 16, 19, and 25. Radiotherapy was recommended for all primary tumour sites and all sites of metastatic disease.

Results: Forty-three patients completed the protocol treatment. Median follow-up for alive patients of the complete cohort was 44.6 months (range 11.5-84.6). For the whole cohort, the 3-year event-free survival (EFS) was 32.3% (95% confidence interval [CI] 23.2-41.6%) with a 3-year overall survival (OS) of 38.4% (95% CI 28.8-47.9%). For localised disease, the 4-year EFS was 39.3% (95% CI 28.2-50.1%) with a 4-year OS of 40.1% (95% CI 28.4-51.5%). For metastatic disease, the 2-year EFS was 8.7% (95% CI 1.5-24.2%) with a 2-year OS of 13.0% (95% CI 3.3-29.7%). Multivariable analysis disclosed that all patients ≤1 year of age were associated with at higher risk of death (hazard ratio [HR]: 2.6; 95% CI 1.0-6.8; p-value = 0.0094). Risk of death was also related with gender in metastatic patients (HR for males: 2.9, 95% CI 1.0-8.0; p-value = 0.0077).

Conclusions: The EpSSG NRSTS 2005 protocol of intensive therapy can be delivered to extracranial MRT patients, with a possible improvement in outcome. The outcome, however, remains poor for patients who progress or with metastatic disease.